As an internal combustion engine for a vehicle including an automobile, a type having a direct injector for injecting fuel into a cylinder and a port injector for injecting fuel into an intake port is known. In such an internal combustion engine, fuel is injected by at least one of the direct injector and the port injector such that a requested fuel injection amount determined based on the engine operating state is achieved. If the direct injector is activated at this time, the direct injector injects an amount of fuel that corresponds to at least some of the requested fuel injection amount is injected by the activation.
Patent Document 1 discloses an internal combustion engine having a direct injector and a port injector. In the disclosed configuration, if the fuel injection amount exceeds the upper limit of a range in which smoke is suppressed when the direct injector injects fuel, the amount of fuel corresponding to the excess over the upper limit is injected by the port injector. Patent Document 2 discloses that, when fuel is injected by a direct injector, the fuel injection is carried out in a divided manner in a shot corresponding to the early stage of the intake stroke and a shot corresponding to the late stage of the intake stroke. In these cases, the amount of fuel to be injected from the direct injector is divided into target fuel injection amounts for respective fuel injection shots in correspondence with a predetermined ratio. The direct injector is then activated such that the respective target fuel injection amounts are achieved.
Specifically, the fuel injection in the late stage of the intake stroke and the fuel injection in the early stage of the intake stroke bring about desirable engine operation, as will be described in the items [1] and [2] below. [1] The fuel injection in the late stage of the intake stroke intensifies the air streams in the cylinder through injected fuel to achieve desirable fuel combustion, when the piston movement speed decreases and thus reduces air stream generation in the cylinder. [2] The fuel injection in the early stage of the intake stroke allows the injected fuel to adhere directly to the piston top and thus cools the piston top using latent heat of vaporization produced by the fuel and suppresses the occurrence of knocking in the engine.